Inter-Calibrating CERES Instrument SW Radiances using Deep Convective Clouds (DCC) within the Same Sun-Synchronous OrbitSun-Synchronous Orbit

The NASA CERES EBAF product provides the scientific community observed TOA fluxes to monitor the Earth’s energy imbalance and validate climate models. To provide a continuous EBAF record, inter-calibration of the Terra, Aqua, and NOAA20 CERES instrument observations is necessary. Currently, the CERES project uses Aqua SNOs to inter-calibrate the NOAA20 and SNPP CERES instruments. The Aqua spacecraft has drifted outside of the 1:30 PM sun-synchronous orbit, limiting the time matched observations with either NOAA20 or SNPP sensors. Deep convective clouds (DCC) are the most Lambertian, brightest, tropical Earth invariant targets located at the tropopause. Since DCC are not susceptible to water vapor absorption for visible wavelengths, this allows the CERES broadband instrument radiances to be easily estimated using VIIRS imager channel radiances. By applying the SNPP VIIRS narrowband to broadband coefficients to the NOAA20 VIIRS radiances and then comparing the resulting broadband radiance with the NOAA20 CERES radiance yields the SNPP and NOAA20 CERES instrument radiometric scaling factors. The SNPP and NOAA20 VIIRS analogous visible channel reflectances are inter-calibrated using the Himawari geostationary imager as a calibration transfer radiometer. Performing the VIIRS and Himawari imager intercalibration using DCC targets during the same month provides consistent VIIRS BT thresholds to identify the DCC targets as well as to mitigate the need to ensure the Himawari visible stability. The CERES instrument radiometric scaling factors will be compared with the factors derived using Aqua CERES.